**Course Title:** Mastering TypeScript: From Basics to Advanced Applications **Section Title:** Classes and Object-Oriented Programming **Topic:** Implementing interfaces in classes Now that we have a solid foundation in classes, constructors, and inheritance in TypeScript, let's dive into another essential concept in object-oriented programming (OOP): interfaces. In this topic, we will explore how to implement interfaces in classes, which will enable us to define a blueprint for our classes and ensure that they conform to a specific contract. **What are interfaces in TypeScript?** As we discussed in the earlier topic on "Working with Types and Interfaces", interfaces in TypeScript are abstract contracts that define a set of properties, methods, and their types. They are used to define the shape of an object, including the properties, methods, and their types. By implementing an interface, a class is bound by a specific contract that it must adhere to. **Why implement interfaces in classes?** Implementing interfaces in classes provides several benefits: * **Contract-based programming**: By implementing an interface, a class guarantees that it will provide a specific set of properties and methods, allowing for a higher degree of decoupling and flexibility in your code. * **Type checking**: The TypeScript compiler will check that the class implementing the interface meets the contract defined by the interface, ensuring that your code is type-safe. * **Abstraction**: Interfaces enable abstraction, which is a fundamental concept in OOP. By defining a contract, you can change the implementation details of a class without affecting other parts of your codebase. **How to implement interfaces in classes** To implement an interface in a class, you use the `implements` keyword followed by the name of the interface. Here's an example: ```typescript interface Printable { print(): void; } class Document implements Printable { print(): void { console.log("Printing document..."); } } ``` In this example, the `Document` class implements the `Printable` interface, which means it must provide an implementation for the `print()` method. The `implements` keyword tells the TypeScript compiler to check that the class meets the contract defined by the interface. If you try to create a class that implements an interface without providing an implementation for all the properties and methods defined by the interface, you will get a compiler error: ```typescript interface Printable { print(): void; } class Document implements Printable { // Error: Class 'Document' incorrectly implements interface 'Printable'. // Property 'print' is missing in type 'Document'. } ``` **Example with multiple interfaces** A class can implement multiple interfaces by listing them after the `implements` keyword, separated by commas: ```typescript interface Printable { print(): void; } interface Shareable { share(): void; } class Document implements Printable, Shareable { print(): void { console.log("Printing document..."); } share(): void { console.log("Sharing document..."); } } ``` In this example, the `Document` class implements both the `Printable` and `Shareable` interfaces, which means it must provide implementations for the `print()` and `share()` methods. **Practical Takeaways** Implementing interfaces in classes is a powerful technique that enables you to define contracts for your classes and ensure that they conform to a specific blueprint. By using interfaces, you can write more robust, maintainable, and scalable code. * **Use interfaces to define contracts**: Define interfaces that specify the properties and methods that a class must implement. * **Implement interfaces in classes**: Use the `implements` keyword to specify that a class implements an interface. * **Ensure that classes meet the contract**: Make sure that the class provides implementations for all the properties and methods defined by the interface. **What's Next?** In the next topic, we will explore advanced TypeScript features, including generics, which enable you to write reusable components. We will cover the concept of generics, how to define generic types, and how to use them to create reusable components. **External Resources** For more information on interfaces and classes in TypeScript, refer to the official TypeScript documentation: * [Interfaces](https://www.typescriptlang.org/docs/handbook/interfaces.html) * [Classes](https://www.typescriptlang.org/docs/handbook/classes.html) **Need Help or Want to Provide Feedback?** Leave a comment below with any questions or feedback about this topic. If you have any suggestions for improving this topic or would like to request additional topics, please let us know.

interface Printable {
  print(): void;
}

class Document implements Printable {
  print(): void {
    console.log("Printing document...");
  }
}

interface Printable {
  print(): void;
}

class Document implements Printable {
  // Error: Class 'Document' incorrectly implements interface 'Printable'.
  // Property 'print' is missing in type 'Document'.
}

interface Printable {
  print(): void;
}

interface Shareable {
  share(): void;
}

class Document implements Printable, Shareable {
  print(): void {
    console.log("Printing document...");
  }

  share(): void {
    console.log("Sharing document...");
  }
}